Electrochemical device and electronic device

Abstract

Electrochemical and electronic devices for improving the high temperature cycle characteristics of electrochemical devices. 【assignment】 [Solution] The electrochemical device of the present invention includes a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector. The positive electrode active material layer includes lithium manganese oxide. The lithium manganese oxide includes aluminum and sodium. When the aluminum content is A% and the sodium content is B% relative to the weight of the positive electrode active material, A and B satisfy 0.01≦A≦2 and 0.001≦B≦1.

Description

Technical Field

[0001] The present invention relates to the field of electrochemistry technology, and specifically to an electrochemical device and an electronic device.

Background Art

[0002] Lithium-ion batteries have many advantages such as large volume and mass energy density, long cycle life, high nominal voltage, low self-discharge rate, small volume, and light weight, and are widely applied in the field of consumer electronics. With the rapid development of electric vehicles and mobile electronic devices in recent years, higher requirements have been put forward for lithium-ion batteries in the market. For example, it is required that lithium-ion batteries remain stable even in a high-temperature environment.

[0003] However, the current lithium-ion batteries have a relatively serious attenuation of specific capacity at high temperatures. This is because high temperature promotes the occurrence of side reactions inside the lithium-ion batteries, resulting in the destruction of the structure of the positive electrode active material and affecting the stability and service life of the lithium-ion batteries. Therefore, there is a need for lithium-ion batteries with a long service life at high temperatures.

Summary of the Invention

[0004] The purpose of the present invention is to provide an electrochemical device and an electronic device for improving the high-temperature cycle characteristics of the electrochemical device. The specific technical solutions are as follows.

[0005] The first aspect of the present invention is an electrochemical device, which includes a positive electrode. The positive electrode includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector. The positive electrode active material layer contains lithium manganese oxide, and the lithium manganese oxide contains aluminum and sodium. When the content of aluminum is A% and the content of sodium is B% based on the weight of the positive electrode active material, A and B satisfy 0.01 ≤ A ≤ 2 and 0.001 ≤ B ≤ 1. An electrochemical device is provided.

[0006] The positive electrode active material layer of the present invention contains lithium manganese oxide, and the lithium manganese oxide contains aluminum and sodium. By controlling the contents of aluminum and sodium within the above ranges, elution of manganese (Mn) can be reduced, and the high-temperature cycle characteristics of the electrochemical device can be improved. Without being limited to any theory, this is because aluminum within the above content range enhances the stability of the Mn-O bond in lithium manganese oxide, improves the crystal structure of lithium manganese oxide, and can reduce the Jahn-Teller effect of the manganese element. Sodium, which is an impurity element, is considered to have little effect on the high-temperature cycle characteristics of the electrochemical device when within the above content range. Therefore, overall, the present invention can reduce the elution of Mn, reduce the influence of sodium on the performance of the positive electrode, and improve the cycle characteristics and storage capacity maintenance characteristics of the electrochemical device by controlling the contents of aluminum and sodium within the above ranges.

[0007] The lithium manganese oxide of the present invention may include, but is not limited to, modified LiMn₂O₄ (hereinafter abbreviated as modified LMO). The modification method of the lithium manganese oxide of the present invention is not particularly limited. For example, aluminum can be incorporated into the lithium manganese oxide of the present invention by adding an aluminum-containing compound during the synthesis of LiMn₂O₄.

[0008] The positive electrode active material layer of the present invention may be provided on at least one surface of the positive electrode current collector. For example, the positive electrode active material layer is provided on one surface of the positive electrode current collector, or the positive electrode active material layer is provided on both surfaces of the positive electrode current collector.

[0009] In one embodiment of the present invention, the electrochemical device of the present invention satisfies at least one of (a) A and B satisfy 0.011 ≦ A + B ≦ 2.5; and (b) A and B satisfy 0.1 ≦ A / B ≦ 125.

[0010] In one embodiment of the present invention, A and B satisfy 0.03 ≦ A + B < 2 and 2 < A / B ≦ 125.

[0011] By controlling the sum of the aluminum content and the sodium content in the positive electrode active material, that is, the value of A + B, within the above range, and / or by controlling the ratio of the aluminum content to the sodium content in the positive electrode active material, that is, the value of A / B, within the above range, an electrochemical device having excellent high-temperature cycle characteristics and storage capacity maintenance characteristics can be obtained.

[0012] In one embodiment of the present invention, the lithium manganese oxide of the present invention further contains niobium. When the content of niobium is C% with respect to the weight of the positive electrode active material, C satisfies 0 < C ≦ 1.

[0013] Without being limited to any theory, niobium within the above content range further improves the crystal structure of lithium manganese oxide, reduces the number of active crystal planes (111) of lithium manganese oxide exposed on the outer surface, that is, reduces the number of active crystal planes (111) in contact with the electrolyte, thereby reducing the side reaction between the electrolyte and the surface of lithium manganese oxide and further reducing the elution of Mn. Thus, the inventors of the present invention have found that the high-temperature cycle characteristics and storage capacity maintenance characteristics of the electrochemical device can be improved. During the modification of lithium manganese oxide, by adding a niobium-containing compound and controlling the addition amount of the niobium-containing compound, the content of niobium in the positive electrode active material layer can be controlled.

[0014] In one embodiment of the present invention, the electrochemical device of the present invention satisfies at least one of (c) to (e) below: (c) A and C satisfy 0.011 < A + C ≤ 2.8; (d) A, B, and C satisfy 0.011 ≤ A + B + C ≤ 3.3; (e) B and C satisfy 0 < C / B ≤ 40. Without being bound by any theory, by controlling the sum of the contents of aluminum and niobium in the positive electrode active material, that is, the value of A + C, within the above range, and / or by controlling the sum of the contents of aluminum, sodium, and niobium in the positive electrode active material, that is, the value of A + B + C, within the above range, and / or by controlling the ratio of the niobium content to the sodium content in the positive electrode active material, that is, the value of C / B, within the above range, an electrochemical device having excellent high-temperature cycle characteristics and storage capacity maintenance characteristics can be obtained.

[0015] In one embodiment of the present invention, A and C satisfy 0.07 ≤ A + C < 2.3.

[0016] By controlling the sum of the contents of aluminum and niobium in the positive electrode active material, that is, the value of A + C, within the above range, more excellent high-temperature cycle characteristics and storage capacity maintenance characteristics can be obtained. In one embodiment of the present invention, when the positive electrode sheet powder of the present invention is measured using X-ray diffraction (XRD), lithium manganate satisfies at least one of (f) to (h) below: (f) lithium manganate shows a first diffraction peak corresponding to the (111) crystal plane at 18° to 20°, and the peak intensity of the first diffraction peak is I(111); (g) lithium manganate shows a second diffraction peak corresponding to the (400) crystal plane at 43° to 45°, and the peak intensity of the second diffraction peak is I(400); (h) lithium manganate shows a third diffraction peak corresponding to the (440) crystal plane at 63° to 65°, and the peak intensity of the third diffraction peak is I(440).

[0017] In one embodiment of the present invention, the electrochemical device of the present invention satisfies at least one of the following: (i) I(400) and I(111) satisfy 0.25 < I(400) / I(111) < 0.55; (j) I(440) and I(400) satisfy 0.35 < I(440) / I(400) < 0.55.

[0018] Without being bound by any theory, by controlling I(400) / I(111) within the above range and / or controlling I(440) / I(400) within the above range, the crystal structure of lithium manganese oxide can be further improved, and the number of active crystal planes (111) of lithium manganese oxide exposed on the outer surface can be reduced, thereby reducing the side reaction between the electrolyte and the surface of lithium manganese oxide, further reducing the elution of Mn, and improving the high-temperature cycle characteristics and storage capacity maintenance characteristics of the electrochemical device. The inventors of the present invention have found this.

[0019] In one embodiment of the present invention, the positive electrode active material layer may further contain lithium nickel cobalt manganese oxide. With respect to the weight of the positive electrode active material, the weight fraction of cobalt is less than 15% or is 15%.

[0020] The positive electrode active material layer of the present invention may further contain lithium nickel cobalt manganese oxide. The base (for example, Li2CO3 or LiOH) remaining on the surface of lithium nickel cobalt manganese oxide reacts with hydrofluoric acid (HF) in the electrolyte to reduce the acidity of the electrolyte and further reduce the elution of Mn, thereby improving the high-temperature cycle characteristics and storage capacity maintenance characteristics of the electrochemical device. Therefore, in the present invention, by controlling the weight fraction of cobalt in the positive electrode active material to be less than 15% or 15% with respect to the weight of the positive electrode active material, the high-temperature cycle characteristics and storage capacity maintenance characteristics of the electrochemical device can be further improved, and the production cost can be reduced.

[0021] In one embodiment of the present invention, the molar ratio of nickel to manganese in the positive electrode active material layer is 0.02:1 to 0.7:1, the molar ratio of cobalt to manganese is less than 0.3:1, or is 0.3:1.

[0022] By controlling the molar ratio of nickel to manganese and the molar ratio of cobalt to manganese in the positive electrode active material layer within the above ranges, nickel, manganese, and cobalt in the positive electrode active material layer can be rationally arranged, and an electrochemical device having excellent high-temperature cycle characteristics and storage capacity maintenance characteristics can be obtained.

[0023] In one embodiment of the present invention, the positive electrode active material layer may further contain lithium iron phosphate (LiFePO4, i.e., LFP), and the average particle diameter of lithium iron phosphate is smaller than the average particle diameter of lithium manganese oxide.

[0024] Without being limited to any theory, because the particle diameter of lithium iron phosphate is small, lithium iron phosphate exists on at least a part of the surface of lithium manganese oxide, that is, lithium manganese oxide may be partially covered with lithium iron phosphate or may be completely covered, thereby suppressing side reactions on the surface of lithium manganese oxide and further improving the high-temperature cycle characteristics and storage capacity maintenance characteristics of the electrochemical device.

[0025] In one embodiment of the present invention, the molar ratio of iron to manganese in the positive electrode active material layer is 0.02:1 to 0.25:1.

[0026] By controlling the molar ratio of iron to manganese in the positive electrode active material layer within the above range, iron and manganese in the positive electrode active material layer are rationally arranged, and side reactions on the surface of lithium manganese oxide are suppressed, thereby further improving the high-temperature cycle characteristics and storage capacity maintenance characteristics of the electrochemical device.

[0027] In one embodiment of the present invention, based on the weight of the positive electrode active material layer, the weight fraction of lithium iron phosphate is ≤ 30%.

[0028] Although not limited to any theory, if the content of lithium iron phosphate is too high in the positive electrode active material layer (for example, exceeding 30%), it will affect the energy density of the electrochemical device. By controlling the weight fraction of lithium iron phosphate in the positive electrode active material layer within the above range, the high-temperature cycle characteristics and storage capacity maintenance characteristics of the electrochemical device can be further improved, and the electrochemical device can be given a high energy density.

[0029] In one embodiment of the present invention, the compression density P of the positive electrode active material layer is 2.7 g / cm 3 ≦P≦4.0 g / cm 3 is satisfied. Although not limited to any theory, if the compression density of the positive electrode active material layer is too low (for example, less than 2.7 g / cm 3 ), it is disadvantageous for improving the energy density of the electrochemical device. If the compression density of the positive electrode active material layer is too high (for example, exceeding 4.0 g / cm 3 ), the positive electrode is likely to undergo brittle fracture, which is disadvantageous for the safety of the electrochemical device. By controlling the compression density of the positive electrode active material layer within the above range, the electrochemical device can be given a high energy density and excellent safety.

[0030] The present invention provides an electrochemical device and an electronic device. The positive electrode of the electrochemical device includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector. The positive electrode active material layer contains lithium manganese oxide, and the lithium manganese oxide contains aluminum and sodium. By controlling the content A% of aluminum and the content B% of sodium in the positive electrode active material to satisfy 0.01≦A≦2 and 0.001≦B≦1, the crystal structure of lithium manganese oxide can be improved, the elution of manganese can be reduced, the cycle characteristics of the electrochemical device, especially the cycle characteristics under high-temperature conditions, can be enhanced, and furthermore, the high-temperature storage characteristics of the electrochemical device can be enhanced.

Brief Description of the Drawings

[0031] To more clearly illustrate the technical solutions of the present invention and the prior art, the following briefly describes the embodiments and the drawings required in the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention.

Figure 1

Embodiments for Carrying Out the Invention

[0032] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be described in more detail below with reference to the drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. For the embodiments of the present invention, all other technical solutions obtained by those skilled in the art fall within the protection scope of the present invention.

[0033] In the specific embodiments of the present invention, the lithium-ion battery is used as an example of the electrochemical device to describe the present invention. However, the electrochemical device of the present invention is not limited to the lithium-ion battery.

[0034] The first aspect of the present invention is an electrochemical device, comprising a positive electrode, the positive electrode including a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector, the positive electrode active material layer including lithium manganese oxide, the lithium manganese oxide including aluminum and sodium. When the content of aluminum is A% and the content of sodium is B% based on the total weight of the positive electrode active material, A and B satisfy 0.01 ≤ A ≤ 2 and 0.001 ≤ B ≤ 1. In one embodiment of the present invention, A and B satisfy 0.49 ≤ A ≤ 1.8 and 0.001 ≤ B < 0.5.

[0035] The positive electrode active material layer of the present invention contains lithium manganese oxide, and the lithium manganese oxide contains aluminum and sodium. By controlling the contents of aluminum and sodium within the above ranges, elution of manganese (Mn) can be reduced, and the high-temperature cycle characteristics of the electrochemical device can be improved. Without being limited by any theory, this is because aluminum within the above content range enhances the stability of the Mn—O bond in the lithium manganese oxide, improves the crystal structure of the lithium manganese oxide, and can reduce the Jahn-Teller effect of the manganese element. It is considered that sodium, which is an impurity element, hardly affects the high-temperature cycle characteristics of the electrochemical device when within the above content range. Therefore, overall, the present invention can reduce the elution of Mn, reduce the influence of sodium on the performance of the positive electrode, and improve the cycle characteristics and storage capacity maintenance characteristics of the electrochemical device by controlling the contents of aluminum and sodium within the above ranges.

[0036] The lithium manganese oxide of the present invention may include, but is not limited to, modified LiMn₂O₄ (hereinafter abbreviated as modified LMO). The method for modifying the lithium manganese oxide of the present invention is not particularly limited. For example, aluminum can be contained in the lithium manganese oxide of the present invention by adding an aluminum-containing compound during the synthesis of LiMn₂O₄.

[0037] The positive electrode active material layer of the present invention may be provided on at least one surface of the positive electrode current collector. For example, the positive electrode active material layer is provided on one surface of the positive electrode current collector, or the positive electrode active material layer is provided on both surfaces of the positive electrode current collector.

[0038] In one embodiment of the present invention, the electrochemical device of the present invention satisfies at least one of (a) A and B satisfy 0.011 ≦ A + B ≦ 2.5, and (b) A and B satisfy 0.1 ≦ A / B ≦ 125. In some examples, A + B is 0.011, 0.03, 0.05, 0.07, 0.1, 0.3, 0.5, 0.9, 1.0, 1.1, 1.3, 1.5, 1.7, 1.9, 2.0, or 2.5, or may be in a range consisting of any two of the above numerical values. In one embodiment of the present invention, A / B is 0.1, 0.3, 0.5, 0.7, 0.9, 1.0, 3.0, 5.0, 7.0, 10, 15, 20, 25, 40, 60, 80, 100, 110, 120, or 125, or may be in a range consisting of any two of the above numerical values.

[0039] Without being limited to any theory, the present invention controls the sum of the aluminum content and the sodium content in the positive electrode active material, that is, the value of A + B, within the above range, and / or controls the ratio of the aluminum content and the sodium content in the positive electrode active material, that is, the value of A / B, within the above range, whereby an electrochemical device having excellent high-temperature cycle characteristics and storage capacity maintenance characteristics can be obtained. If A / B is too large, the improvement in the cycle characteristics of the electrochemical device is slight, and if the value of A / B is too small, it may affect the reversible capacity of the electrochemical device.

[0040] In one embodiment of the present invention, the lithium manganese oxide further contains niobium. When the content of niobium is C% with respect to the total weight of the positive electrode active material, C satisfies 0 < C ≦ 1. In some examples, C satisfies 0.0001 ≦ C ≦ 0.7. In some examples, C satisfies 0.0001 ≦ C ≦ 0.5. In some examples, C is 0.001, 0.003, 0.005, 0.008, 0.1, 0.3, 0.5, 0.7, 0.9, or 1.0, or may be in a range consisting of any two of the above numerical values.

[0041] Although not limited to any theory, niobium within the above content range can further improve the crystal structure of lithium manganese oxide, reduce the number of active crystal planes (111) of lithium manganese oxide exposed on the outer surface, that is, reduce the number of active crystal planes (111) in contact with the electrolytic solution, thereby reducing the side reaction between the electrolytic solution and the surface of lithium manganese oxide, further reducing the elution of Mn, and thereby improving the high-temperature cycle characteristics and storage capacity maintenance characteristics of the electrochemical device. The inventors of the present invention have found. During the modification of lithium manganese oxide, by adding a niobium-containing compound and controlling the addition amount of the niobium-containing compound, the content of niobium in the positive electrode active material layer can be controlled. In the present invention, the niobium-containing compound is not particularly limited, and may include, for example, but not limited to, Nb2O5 and NbF5.

[0042] In one embodiment of the present invention, in the electrochemical device of the present invention, A and C satisfy 0.01 < A + C ≤ 2.8. In some examples, A and C satisfy 0.011 < A + C ≤ 2. In some examples, A and C satisfy 0.07 ≤ A + C ≤ 2.3. In some examples, A and C satisfy 0.01 ≤ A + C ≤ 1.6. In some examples, A + C is 0.011, 0.03, 0.05, 0.07, 0.09, 0.1, 0.3, 0.5, 0.7, 0.9, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, or 2.8, or may be in the range consisting of any two of the above numerical values.

[0043] By controlling the sum of the contents of aluminum and niobium in the positive electrode active material, that is, the value of A + C, within the above range, the characteristics of the electrochemical device are in a relatively excellent state. If the value of A + C is too high, the improvement of the cycle characteristics of the electrochemical device is slight, and it may affect the reversible capacity of the electrochemical device.

[0044] In one embodiment of the present invention, for the electrochemical device of the present invention, A, B, and C satisfy 0.011 ≦ A + B + C ≦ 3.3. In some embodiments, A, B, and C satisfy 0.1 ≦ A + B + C ≦ 2.0. In some embodiments, A + B + C is 0.011, 0.05, 0.07, 0.1, 0.3, 0.5, 0.7, 0.9, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.5, 3.0, or 3.3, or may be in a range consisting of any two of the above numerical values.

[0045] By controlling the value of A + B + C within the above range, the electrochemical device has excellent cycle characteristics and storage characteristics.

[0046] In one embodiment of the present invention, for the electrochemical device of the present invention, B and C satisfy 0 < C / B ≦ 40. In some embodiments, B and C satisfy 0 < C / B ≦ 10. In some embodiments, B and C satisfy 0 < C / B ≦ 5. In some embodiments, B and C satisfy 0 < C / B ≦ 3. In some embodiments, C / B is 0.0001, 0.0005, 0.001, 0.003, 0.005, 0.007, 0.009, 0.01, 0.03, 0.05, 0.07, 0.09, 0.1, 0.3, 0.5, 0.7, 0.9, 1.0, 1.2, 1.5, 1.7, 1.9, 2.0, 3.0, 5.0, 7.0, 9.0, 10.0, 15, 20, 25, 30, 35, or 40, or may be in a range consisting of any two of the above numerical values.

[0047] By controlling the value of C / B within the above range, an electrochemical device having excellent high-temperature cycle characteristics and storage capacity maintenance characteristics can be obtained. If the value of C / B is too high, it may affect the cycle characteristics of the electrochemical device. If the value of C / B is too low, the protection for the lithium manganese oxide active crystal plane (111) is small, the suppression of Mn elution is slight, and the loss of the reversible capacity of the electrochemical device may increase.

[0048] In one embodiment of the present invention, when the positive electrode sheet powder of the present invention is measured using X-ray diffraction (XRD), lithium manganese oxide shows a first diffraction peak corresponding to the (111) crystal plane at 18° to 20°, and the peak intensity of the first diffraction peak is I(111).

[0049] In one embodiment of the present invention, when the positive electrode sheet powder of the present invention is measured using X-ray diffraction (XRD), lithium manganese oxide shows a second diffraction peak corresponding to the (400) crystal plane at 43° to 45°, and the peak intensity of the second diffraction peak is I(400).

[0050] In one embodiment of the present invention, when the positive electrode sheet powder of the present invention is measured using X-ray diffraction (XRD), lithium manganese oxide shows a third diffraction peak corresponding to the (440) crystal plane at 63° to 65°, and the peak intensity of the third diffraction peak is I(440).

[0051] The positive electrode sheet of the present invention includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode active material, the main component of the positive electrode active material is lithium manganese oxide, and by XRD measurement, the lithium manganese oxide of the present invention includes the (111) crystal plane, the (400) crystal plane, and the (440) crystal plane.

[0052] In one embodiment of the present invention, for the electrochemical device of the present invention, I(400) and I(111) satisfy 0.25 < I(400) / I(111) < 0.55.

[0053] In one embodiment of the present invention, for the electrochemical device of the present invention, I(440) and I(400) satisfy 0.35 < I(440) / I(400) < 0.55.

[0054] Without being limited to any theory, by controlling I(400) / I(111) within the above range and / or controlling I(440) / I(400) within the above range, the crystal structure of lithium manganese oxide can be further improved, and by reducing the number of active crystal planes (111) of lithium manganese oxide exposed on the outer surface, the side reaction between the electrolyte and the surface of lithium manganese oxide can be reduced, the elution of Mn can be further reduced, and the high-temperature cycle characteristics and storage capacity maintenance characteristics of the electrochemical device can be improved.

[0055] In one embodiment of the present invention, the positive electrode active material further contains an M element, and the M element contains at least one of Cu, Fe, Mg, Ti, Zr, Zn, W, Sr, and Y. In some examples, the M element may contain Mg and at least one of Cu, Fe, Ti, Zr, Zn, W, Sr, and Y.

[0056] In one embodiment of the present invention, based on the weight of the positive electrode active material, the content of the M element is less than 5% or is 5%. In some examples, the content of the M element is 0.01%, 0.03%, 0.05%, 0.07%, 0.1%, 0.3%, 0.5%, 0.7%, 1.0%, 2.0%, 3.0%, or 5.0%, or may be in the range consisting of any two of the above numerical values.

[0057] In one embodiment of the present invention, the positive electrode active material further contains an X element, and the X element contains at least one of S, P, B, F, and Cl.

[0058] In one embodiment of the present invention, based on the weight of the positive electrode active material, the content of the X element is less than 3% or is 3%. In some examples, the content of the X element is 0.01%, 0.03%, 0.05%, 0.07%, 0.1%, 0.3%, 0.5%, 0.7%, 1.0%, 2.0%, or 3.0%, or may be in the range consisting of any two of the above numerical values.

[0059] In one embodiment of the present invention, the positive electrode active material layer may further contain lithium nickel cobalt manganese oxide, and the weight fraction of cobalt is less than 15% or 15% based on the weight of the positive electrode active material.

[0060] Without being bound by any theory, the positive electrode active material layer of the present invention may further contain lithium nickel cobalt manganese oxide. The base (for example, Li2CO3 or LiOH) left on the surface of the lithium nickel cobalt manganese oxide reacts with hydrofluoric acid (HF) in the electrolyte to reduce the acidity of the electrolyte and further reduce the elution of Mn, thereby improving the high-temperature cycle characteristics and storage capacity maintenance characteristics of the electrochemical device. If the cobalt content is too high, it will lead to an increase in the production cost of the electrochemical device. Therefore, in the present invention, by controlling the weight fraction of cobalt in the lithium nickel cobalt manganese oxide to be less than 15% or 15% based on the weight of the positive electrode active material, the high-temperature cycle characteristics and storage capacity maintenance characteristics of the electrochemical device can be further improved, and the production cost can be reduced.

[0061] The lithium nickel cobalt manganese oxide in the present invention is not particularly limited as long as the object of the present invention can be achieved. For example, the lithium nickel cobalt manganese oxide may be lithium nickel cobalt manganese oxide (hereinafter abbreviated as NCM). The lithium nickel cobalt manganese oxide may be single-crystal lithium nickel cobalt manganese oxide or polycrystalline lithium nickel cobalt manganese oxide.

[0062] In one embodiment of the present invention, the molar ratio of nickel to manganese in the positive electrode active material layer is 0.02:1 to 0.7:1.

[0063] In one embodiment of the present invention, the molar ratio of nickel to manganese in the positive electrode active material layer is less than 0.3:1 or 0.3:1.

[0064] In the present invention, by controlling the molar ratios of nickel to manganese and cobalt to manganese in the positive electrode active material layer within the above ranges, nickel, manganese, and cobalt in the positive electrode active material layer can be rationally arranged, and an electrochemical device having excellent high-temperature cycle characteristics and storage capacity maintenance characteristics can be obtained.

[0065] In one embodiment of the present invention, the positive electrode active material layer may further contain lithium iron phosphate (LiFePO4, i.e., LFP), and the average particle diameter of lithium iron phosphate is smaller than the average particle diameter of lithium manganese oxide.

[0066] In one embodiment of the present invention, the average particle diameter of lithium iron phosphate is smaller than 2 μm, or is 2 μm. In some examples, the average particle diameter of lithium iron phosphate is smaller than 1.8 μm, or is 1.8 μm. In some examples, the average particle diameter of lithium iron phosphate is smaller than 1.5 μm, or is 1.5 μm. In some examples, the average particle diameter of lithium iron phosphate is smaller than 1.2 μm, or is 1.2 μm. In some examples, the average particle diameter of lithium iron phosphate is smaller than 1.0 μm, or is 1.0 μm.

[0067] One embodiment of the present invention utilizes the feature that the particle diameter of lithium iron phosphate is small, and makes lithium iron phosphate exist on at least a part of the surface of lithium manganese oxide, that is, lithium manganese oxide may be partially or entirely covered with lithium iron phosphate, thereby suppressing side reactions on the surface of lithium manganese oxide and further improving the high-temperature cycle characteristics and storage capacity maintenance characteristics of the electrochemical device.

[0068] In one embodiment of the present invention, the molar ratio of iron to manganese in the positive electrode active material layer is 0.02:1 to 0.25:1. In some embodiments, the molar ratio of iron to manganese in the positive electrode active material layer is 0.03:1 to 0.13:1. In some embodiments, the molar ratio of iron to manganese in the positive electrode active material layer is 0.05:1 to 0.12:1. In some embodiments, the molar ratio of iron to manganese in the positive electrode active material layer is 0.03:1 to 0.13:1.

[0069] By controlling the molar ratio of iron to manganese in the positive electrode active material layer within the above range, iron and manganese in the positive electrode active material layer can be reasonably arranged, side reactions on the surface of lithium manganese oxide can be suppressed, and the high-temperature cycle characteristics and storage capacity maintenance characteristics of the electrochemical device can be further improved.

[0070] In one embodiment of the present invention, based on the weight of the positive electrode active material layer, the weight fraction of lithium iron phosphate is ≤30%.

[0071] Without being limited by any theory, if the content of lithium iron phosphate is too high in the positive electrode active material layer (for example, exceeding 30%), it will affect the energy density of the electrochemical device. By controlling the weight fraction of lithium iron phosphate in the positive electrode active material layer within the above range, the high-temperature cycle characteristics and storage capacity maintenance characteristics of the electrochemical device can be further improved, and the electrochemical device can be given a high energy density.

[0072] In one embodiment of the present invention, the compression density P of the positive electrode active material layer is 2.7 g / cm 3 ≤P≤4.0 g / cm 3 is satisfied. Without being limited by any theory, if the compression density of the positive electrode active material layer is too low (for example, less than 2.7 g / cm 3 ), it is disadvantageous for improving the energy density of the electrochemical device. If the compression density of the positive electrode active material layer is too high (for example, 4.0 g / cm 3If it exceeds (a certain value), the positive electrode is prone to brittle fracture, which is disadvantageous for the safety of the electrochemical device. By controlling the compression density of the positive electrode active material layer within the above range, the electrochemical device can be provided with a high energy density and excellent safety.

[0073] The preparation method of lithium manganese oxide in the present invention is not particularly limited, and a preparation method known to those skilled in the art can be adopted. For example, in the process of synthesizing lithium manganese oxide, an aluminum-containing compound (such as Al2O3, Al(OH)3, AlF3) can be added to LiMn2O4 to obtain the above-mentioned lithium manganese oxide, that is, modified LMO. In addition, in the present invention, by controlling the addition amount of the aluminum-containing compound, for example, and adjusting the aluminum content in the lithium manganese oxide, the change in the aluminum content in the positive electrode active material layer can be achieved. By adjusting the sodium content in the precursor of LiMn2O4, the change in the sodium content in the positive electrode active material layer can be achieved. In the present invention, the adjustment process is not specifically limited, as long as the object of the present invention can be achieved.

[0074] The positive electrode sheet in the present invention is not particularly limited, as long as the object of the present invention can be achieved. For example, the positive electrode sheet usually includes a positive electrode current collector and a positive electrode active material layer. The positive electrode current collector is not particularly limited, and may be any positive electrode current collector in the art, such as aluminum foil, aluminum alloy foil or composite current collector.

[0075] The negative electrode sheet in the present invention is not particularly limited as long as the object of the present invention can be achieved. For example, the negative electrode sheet usually includes a negative electrode current collector and a negative electrode active material layer. The negative electrode current collector is not particularly limited, and materials such as metal foil materials or expanded metals can be used. For example, it is a foil material or a porous plate of a metal such as copper, nickel, titanium, or iron or an alloy thereof, for example, a copper foil. The negative electrode active material layer includes a negative electrode active material, a conductive agent, an adhesive, and a thickener. The negative electrode active material is not particularly limited, and any negative electrode active material in the art can be used. For example, artificial graphite, natural graphite, mesocarbon microbeads (MCMB), soft carbon, hard carbon, silicon, silicon-carbon, SiO, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, lithium titanate with a spinel structure Li4Ti5O 12 , may include at least one of Li-Al alloy and metallic lithium. The conductive agent may be at least one of graphite, superconducting carbon, acetylene black, carbon black, ketjen black, carbon dot, carbon nanotube, graphene, and carbon nanofiber. The adhesive may be at least one of styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), water-based acrylic resin, and carboxymethyl cellulose (CMC). The thickener may be carboxymethyl cellulose (CMC).

[0076] The base material of the separator of the present invention includes, but is not limited to, at least one selected from polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyimide (PI), and aramid. For example, polyethylene contains at least one component selected from high-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene. In particular, polyethylene and polypropylene have an excellent effect of preventing short circuits and can improve the stability of the electrochemical device by the shutdown effect. The base material may have a single-layer structure or a multilayer composite structure in which multiple types are mixed. The thickness is 3 μm to 20 μm.

[0077] The lithium-ion battery of the present invention further includes an electrolyte, and the electrolyte may be at least one of a gel electrolyte, a solid electrolyte, and an electrolytic solution. The electrolytic solution contains a lithium salt and a non-aqueous solvent. In some embodiments of the present invention, the lithium salt is at least one selected from LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, and lithium difluoroborate. For example, LiPF6 can be selected as the lithium salt because it can provide high ionic conductivity and improve cycle characteristics. The non-aqueous solvent may be a carbonate compound, a carboxylic acid ester compound, an ether compound, other organic solvents, or a combination thereof. The carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluorocarbonate compound, or a combination thereof. Examples of the chain carbonate compound are dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and combinations thereof. Examples of the cyclic carbonate compound are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), and combinations thereof. Examples of the fluorocarbonate compound are fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethyl ethylene carbonate, and combinations thereof.Examples of the carboxylic acid ester compound include methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decalactone, valerolactone, mevalonic acid lactone, caprolactone, and combinations thereof. Examples of the ether compound include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof. Examples of the other organic solvents include dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters, and combinations thereof.

[0078] A second aspect of the present invention provides an electronic device including the electrochemical device described in the above-described embodiment of the present invention.

[0079] The electronic device of the present invention is not particularly limited and may be any known electronic device used in the prior art. In some embodiments, the electronic device can include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an e-book player, a mobile phone, a portable facsimile, a portable copier, a portable printer, a stereo headset, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disk, a transceiver, an electronic organizer, a calculator, a memory card, a portable tape recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, an assist bicycle, a bicycle, a lighting fixture, a toy, a game machine, a watch, a power tool, a flash, a camera, a large household storage battery, and a lithium ion capacitor.

[0080] The preparation process of the electrochemical device is well-known to those skilled in the art and is not particularly limited in the present invention. For example, a lithium-ion battery can be manufactured by stacking a positive electrode and a negative electrode with a separator in between, performing operations such as winding or folding it as necessary, placing it in a case, and injecting an electrolyte into the case and sealing it. Additionally, an overcurrent prevention element, lead plate, etc. can be placed in the case as necessary to prevent an increase in pressure inside the lithium-ion battery, overcharging, and overdischarging.

[0081] The present invention provides an electrochemical device and an electronic device. The positive electrode of the electrochemical device includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector. The positive electrode active material layer contains lithium manganese oxide, the lithium manganese oxide contains aluminum and sodium, and by controlling the content A% of aluminum and the content B% of sodium in the positive electrode active material to satisfy 0.01 ≦ A ≦ 2 and 0.001 ≦ B ≦ 1, the crystal structure of the lithium manganese oxide can be improved, the elution of manganese can be reduced, the cycle characteristics of the electrochemical device, particularly the cycle characteristics under high-temperature conditions, can be enhanced, and furthermore, the high-temperature storage characteristics of the electrochemical device can be enhanced.

[0082] Measurement method and apparatus: Measurement of the element content of the positive electrode active material layer: A lithium-ion battery discharged to a voltage of 2.8 V was disassembled. Then, the positive electrode active material layer on the dried positive electrode sheet was dissolved in a mixed solvent (for example, a mixed solvent of 10 ml of aqua regia (a mixture of nitric acid and hydrochloric acid in a 1:1 ratio) and 2 ml of HF was used for 0.4 g of the positive electrode active material), made up to 100 mL, and then the content of elements such as Al, Na, and Nb in the solution was measured using an ICP (Inductively coupled plasma) analyzer.

[0083] XRD measurement: The lithium-ion battery discharged to a voltage of 2.8 V was disassembled. Then, the positive electrode sheet was taken out, the positive electrode active material layer was scraped off with a doctor blade to obtain the positive electrode active material layer powder. After that, the positive electrode active material layer powder was placed on the sample stage of an XRD measuring device (model: Bruker, D8), and an XRD diffraction pattern was obtained at a scanning speed of 2° / min and a scanning angle range of 10° to 90°. Peak values corresponding to the characteristic peaks (111), (400), and (440) of lithium manganese oxide were taken from the XRD diffraction pattern. Next, the ratio of I(400) to I(111) was obtained and denoted as I(400) / I(111), and the ratio of I(440) to I(400) was denoted as I(440) / I(400).

[0084] Measurement of the particle size of the particles in the positive electrode active material layer: The lithium-ion battery discharged to a voltage of 2.8 V was disassembled. Then, the dried positive electrode sheet was sliced, and the sliced cross-section was observed using a scanning electron microscope (SEM) to search for particles in the cross-section. After that, the components of single particles were determined using an energy dispersive X-ray analyzer (EDS), and the particle size of the single particles was measured using SEM at a magnification of 1000 times. Three images were selected and the average value was calculated. The measuring device is OXFORD EDS (X-max-20mm 2 )

[0085] Measurement of the compression density of the positive electrode active material layer: The lithium-ion battery discharged to a voltage of 2.8 V was disassembled. Then, the positive electrode sheet was taken out, and the positive electrode sheet was immersed in DMC (dimethyl carbonate) for 30 min to remove the electrolyte and by-products on the surface of the positive electrode sheet. After that, it was dried in a draft chamber for 4 hours. After drying, the positive electrode sheet was taken out, five positive electrode sheets with a size of 5 cm × 5 cm were selected, and the thickness of each positive electrode sheet was measured with a micrometer with an accuracy of 0.0001 mm and denoted as d0. The positive electrode active material layer of the positive electrode sheet was scraped off with a doctor blade, and the weight of the positive electrode active material layer was weighed with a balance and denoted as m. The thickness of the current collector from which the active material was removed was measured with a micrometer with an accuracy of 0.0001 mm and denoted as d. The compression density of the positive electrode active material layer was calculated according to the following formula. Compression density P = m / [5 cm × 5 cm × (d0 - d)], unit g / cm3 . The compression density of the positive electrode active material layer is the average value of five positive electrode plates.

[0086] Measurement of the capacity of the lithium-ion battery: Four lithium-ion batteries were taken and charged at a charging current of 0.5C until the upper limit voltage reached 4.2V in an environment of 25°C. Then, constant current discharge was performed at a discharge current of 0.2C until the final voltage reached 2.8V, and the initial discharge capacity at 0.2C was calculated as the capacity of this lithium-ion battery.

[0087] Measurement of the cycle characteristics of the lithium-ion battery: Charging and discharging were repeated for the lithium-ion battery according to the following procedure, and the discharge capacity retention rate of the lithium-ion battery was calculated. In an environment of 25°C, the first charging and discharging were performed. Charging was carried out at a charging current of 0.5C until the voltage reached 4.2V, and then constant current discharge was performed at a discharge current of 1C until the final voltage reached 2.8V. The discharge capacity was recorded as the discharge capacity of the first cycle. Then, the above procedure was repeated to perform 1000 cycles of charging and discharging, and the discharge capacity of the 1000th cycle was recorded. 25°C cycle capacity retention rate = (discharge capacity of the 1000th cycle / discharge capacity of the first cycle) × 100%. In an environment of 45°C, charging was carried out at a charging current of 0.5C until the voltage reached 4.2V, and then constant current discharge was performed at a discharge current of 1C until the final voltage reached 2.8V. The discharge capacity was recorded as the discharge capacity of the first cycle. Then, the above procedure was repeated to perform 500 cycles of charging and discharging, and the discharge capacity of the 500th cycle was recorded. 45°C cycle capacity retention rate = (discharge capacity of the 500th cycle / discharge capacity of the first cycle) × 100%.

[0088] Measurement of the high-temperature storage characteristics of the lithium-ion battery: In an environment of 25°C, charging was carried out at a charging current of 0.5C until the upper limit voltage reached 4.2V, and then constant current discharge was performed at a discharge current of 1C until the final voltage reached 2.8V. The discharge capacity was recorded as the capacity before storage. Charge at a constant current of 0.5C until the voltage reaches 3.85V, then charge at a constant voltage of 4.2V until the current is less than 0.05C. Place the battery in an oven at 60°C and store for 14 days. Then, perform constant-current discharge at a discharge current of 1C until the final voltage reaches 2.8V. After that, charge at a charging current of 0.5C until the voltage reaches 4.2V. Then, perform constant-current discharge at a discharge current of 1C until the voltage reaches 2.8V. Record the battery discharge capacity and use it as the capacity after storage. Capacity retention rate of lithium-ion battery = Capacity after storage / Capacity before storage × 100%.

[0089] Example 1 <Preparation of Lithium Manganate> Weigh 203.3 g of lithium carbonate (among which the lithium content is 18.71%), 1000.0 g of manganese dioxide (among which the Mn content is 60.22% and the Na content is 0.27%), and 29.96 g of aluminum trioxide (aluminum content 52.91%). Mix them in a high-speed mixer at 300 r / min for 20 min. Place the mixture in an air kiln, heat it to 820°C at a rate of 5°C / min, hold for 24 hours, take it out after natural cooling, pass it through a 300-mesh sieve, and obtain lithium manganate (i.e., modified LMO).

[0090] <Preparation of Positive Electrode Plate> Mix the obtained positive electrode active material, polyvinylidene fluoride (PVDF) as an adhesive, conductive carbon black, and carbon nanotubes (CNT) in a weight ratio of 95:2:1.8:1.2. Then, add NMP (N-methylpyrrolidone) as a solvent and prepare a positive electrode slurry that is uniform, transparent, and has a solid content of 75% under vacuum stirring. Uniformly coat the positive electrode slurry on one surface of an aluminum foil with a thickness of 9 μm, dry it under the condition of 90°C, and cold roll it to obtain a positive electrode plate with a total thickness of 100 μm for the positive electrode active material layer. Then, repeat the above procedure on the other surface of this positive electrode plate to obtain a positive electrode plate with the positive electrode active material layer coated on both sides. Cut the positive electrode plate into a size of 74 mm × 867 mm, weld the tabs, and let it stand. Among them, the aluminum content in the positive electrode active material layer is 1.52%, the sodium content is 0.26%, and the compression density of the positive electrode active material layer is 2.8 g / cm 3 was.

[0091] <Preparation of the negative electrode sheet> Artificial graphite, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) as the negative electrode active material were mixed at a weight ratio of 98:1:1. Then, deionized water was added as a solvent to prepare a slurry with a solid content of 70 wt%, and it was uniformly stirred. The slurry was uniformly coated on one surface of a copper foil with a thickness of 8 μm, dried under the condition of 110 °C, and cold-rolled to obtain a negative electrode sheet with a negative electrode active material layer coated on one side with a thickness of 150 μm. Then, the above coating procedure was repeated on the other surface of this negative electrode sheet to obtain a negative electrode sheet with negative electrode active material layers coated on both sides. The negative electrode sheet was cut into a size of 74 mm × 867 mm, tabs were welded, and it was left standing.

[0092] <Preparation of the separator> A polyethylene (PE) porous polymer film with a thickness of 15 μm was used as the separator.

[0093] <Preparation of the electrolyte> Under an environment with a water content of less than 10 ppm, propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC), which are non-aqueous organic solvents, were mixed at a weight ratio of 1:1:1. Then, lithium hexafluorophosphate (LiPF6) was added to the non-aqueous organic solvent and dissolved, and it was uniformly mixed. The molar concentration of LiPF6 in the electrolyte was 1.15 mol / L. 2% of fluoroethylene carbonate, 2% of ethylene carbonate, and 1% of ethylene sulfate were added to the total weight of the electrolyte and uniformly mixed to prepare the electrolyte.

[0094] <Preparation of the lithium-ion battery> The positive electrode sheet, separator, and negative electrode sheet prepared above were stacked in sequence, with the separator positioned between the positive electrode sheet and the negative electrode sheet to play a role of isolation, and they were wound up to obtain an electrode assembly. The electrode assembly was placed in an aluminum laminated film packaging bag, the moisture was removed at 80 °C, the prepared electrolyte was injected, and through processes such as vacuum sealing, standing, formation, and shaping, a lithium-ion battery was obtained.

[0095] Examples 2 to 7 Similar to the preparation method of Example 1, the differences were in the element contents and the particle size of lithium manganese oxide shown in Tables 1 to 2.

[0096] Example 8 Similar to the preparation method of Example 1, the difference was that 850.3 g of trimanganese tetraoxide was used instead of 1000.0 g of manganese dioxide, and the differences in other parameters are shown in Tables 1 to 2.

[0097] Example 9 Similar to the preparation method of Example 1, the difference was that a niobium-containing compound Nb2O5 was added to lithium manganese oxide, and the aluminum content in the positive electrode active material layer was adjusted to 1.01%, the sodium content to 0.26%, and the niobium content to 0.09%. Except for adjusting the compression density of the positive electrode active material layer to 3.0 g / cm 3 , it was the same as the preparation method of Example 1.

[0098] Example 10 Similar to the preparation method of Example 9, the differences were in the element contents and the particle size of lithium manganese oxide shown in Tables 1 to 2.

[0099] Example 11 203.3 g of lithium carbonate (among which, lithium content 18.71%), 850.3 g of trimanganese tetraoxide (among which, Mn content 70.82%, Na content 0.01%), 19.10 g of aluminum oxide (aluminum content 52.91%), 2.87 g of niobium pentoxide (niobium content 79.46%) were weighed, mixed in a high-speed mixer at 300 r / min for 20 min, the mixture was placed in an air kiln, heated to 750 °C at 5 °C / min, held for 24 h, taken out after natural cooling, passed through a 300-mesh sieve, and a lithium manganese oxide (i.e., modified LMO) product was obtained.

[0100] Examples 12 to 13 Similar to the preparation method of Example 11, the differences were in the element contents and the particle size of lithium manganese oxide shown in Tables 1 to 2.

[0101] Examples 14 to 21 Similar to the preparation method of Example 9, the differences were in the element contents and the particle diameters of lithium manganese oxide shown in Tables 1 to 2.

[0102] Example 22 Modified LMO as the positive electrode active material (its preparation method was similar to that of Example 9, and the differences were in the element contents and particle diameters shown in Tables 1 to 2) and polycrystalline lithium nickel cobalt manganese oxide with an average particle diameter of 15.3 μm (LiNi 0.60 Co 0.10 Mn 0.30 O2, denoted as NCM: 15.8 (601030)) were mixed to obtain a mixture, and the mixture was formulated according to the parameters shown in Tables 1 to 2 so that the molar ratios of nickel to manganese and cobalt to manganese satisfied the ratios shown in Tables 1 to 2. The element contents and particle diameters in the positive electrode active material layer were shown in Tables 1 to 2, and the tap density of the positive electrode active material layer was 3.3 g / cm 3 It was the same as Example 9 except for this.

[0103] Examples 23 to 33 Similar to the preparation method of Example 22, the differences were that parameters such as the element contents, the average particle diameter of modified LMO, the type and average particle diameter of polycrystalline lithium nickel cobalt manganese oxide, the molar ratio of nickel to manganese, and the molar ratio of cobalt to manganese were adjusted as shown in Tables 1 to 2.

[0104] Example 34 Modified LMO as the positive electrode active material (its preparation method was similar to that of Example 11, and the differences were in the element contents and particle diameters shown in Tables 1 to 2) and polycrystalline lithium nickel cobalt manganese oxide with an average particle diameter of 15.3 μm (LiNi 0.50 Co 0.20 Mn 0.30Denoted as O2 and NCM: 15.9 (502030)) were mixed to obtain a mixture. The ratio of LMO and NCM was adjusted so that the molar ratio of nickel to manganese and the molar ratio of cobalt to manganese satisfied the ratios shown in Tables 1 - 2. The element contents and particle sizes in the positive electrode active material layer are shown in Tables 1 - 2. Otherwise, it was the same as in Example 11.

[0105] Example 35 Modified LMO, which is a positive electrode active material (its preparation method is similar to that of Example 11, and the differences lie in the element contents and particle sizes shown in Tables 1 - 2), and lithium iron phosphate (abbreviated as LFP) with an average particle size of 1 μm were mixed to obtain a mixture. The ratio of LMO and LFP was adjusted so that the molar ratio of iron to manganese satisfied the ratio shown in Tables 1 - 2. The element contents and particle sizes in the positive electrode active material layer are shown in Tables 1 - 2. Otherwise, it was the same as in Example 11.

[0106] Example 36 Similar to the preparation method of Example 35, the differences were in the parameters shown in Tables 1 - 2.

[0107] Example 37 Modified LMO, which is a positive electrode active material (its preparation method is similar to that of Example 9, and the differences lie in the element contents and particle sizes shown in Tables 1 - 2), and polycrystalline lithium nickel cobalt manganese oxide with an average particle size of 16.2 μm (LiNi 0.55 Co 0.15 Mn 0.30 O2, denoted as NCM: 16.2 (551530)) and lithium iron phosphate (abbreviated as LFP) with an average particle size of 1 μm were mixed to obtain a mixture. The molar ratio of nickel to manganese and the molar ratio of cobalt to manganese satisfied the ratios shown in Tables 1 - 2. The element content and particle size in the positive electrode active material layer are shown in Tables 1 - 2, and the compression density of the positive electrode active material layer was 3.3 g / cm 3 It was. Otherwise, it was the same as in Example 9.

[0108] Example 38 Modified LMO as the positive electrode active material (its preparation method is similar to Example 11, and the differences lie in the element content and particle size shown in Tables 1 to 2) and single-crystalline lithium nickel cobalt manganese oxide with an average particle size of 6.4 μm (LiNi 0.55 Co 0.15 Mn 0.30 O2, denoted as NCM: 6.4(551530)) and lithium iron phosphate with an average particle size of 1 μm (abbreviated as LFP) were mixed to obtain a mixture, and the molar ratio of nickel to manganese and the molar ratio of cobalt to manganese satisfied the ratios shown in Tables 1 to 2. Otherwise, it was the same as in Example 11.

[0109] Example 39 Modified LMO as the positive electrode active material (its preparation method is similar to Example 9, and the differences lie in the element content and particle size shown in Tables 1 to 2) and polycrystalline lithium nickel cobalt manganese oxide with an average particle size of 16.2 μm (LiNi 0.55 Co 0.15 Mn 0.30 O2, denoted as NCM: 16.2(551530)) and lithium iron phosphate with a particle size of 1 μm (abbreviated as LFP) were mixed to obtain a mixture, and the molar ratio of nickel to manganese and the molar ratio of cobalt to manganese satisfied the ratios shown in Tables 1 to 2. Otherwise, it was the same as in Example 9.

[0110] Examples 40 to 41 The preparation method was similar to Example 9, and the differences were in the parameters shown in Tables 1 to 2.

[0111] Comparative Example 1 It was the same as in Example 1 except that the positive electrode active material was LiMn2O4 without aluminum doping.

[0112] Comparative Example 2 It was the same as in Example 22 except that the positive electrode active material was LiMn2O4 without aluminum doping.

[0113] Comparative Example 3 It was the same as in Example 37 except that the positive electrode active material was LiMn2O4 without aluminum doping.

[0114] Comparative Example 4 It was the same as Example 9 except that the elemental content of the positive electrode active material was adjusted as shown in Tables 1 to 2.

[0115] Comparative Example 5 It was the same as Example 9 except that the elemental content of the positive electrode active material was adjusted as shown in Tables 1 to 2.

[0116] [Table 1]

[0117] [Table 2]

[0118] Among them, the parameters of the combinations of A, B, and C are shown in Tables 3 to 4: [Table 3]

[0119] [Table 4]

[0120] In Tables 1 to 2 and Tables 3 to 4, " / " indicates that it is not contained or not measured.

[0121] As can be seen from Examples 1 to 8 and Comparative Example 1, the lithium-ion battery of the present invention having an aluminum content A% and a sodium content B% in the positive electrode active material layer and satisfying 0.01 ≦ A ≦ 2 and 0.001 ≦ B ≦ 1 has clearly improved in all of the 25°C cycle capacity retention rate, 45°C cycle capacity retention rate, and storage capacity retention rate, indicating that the lithium-ion battery of the present invention has excellent cycle characteristics, particularly high-temperature cycle characteristics, and excellent high-temperature storage characteristics.

[0122] From Examples 1 to 8 and Comparative Examples 1 to 3, when the lithium manganese oxide of the present invention is not contained in the positive electrode active material (for example, Comparative Examples 1 to 3), it was found that I(400) / I(111) and I(440) / I(400) exceeded the scope of the present invention. On the other hand, it was found that the lithium ion battery having the ranges of I(400) / I(111) and I(440) / I(400) of the present invention has excellent cycle characteristics, particularly high temperature cycle characteristics, and excellent high temperature storage characteristics.

[0123] From Examples 9 to 21 and Comparative Examples 4 to 5, when the aluminum content in the positive electrode active material is too high (for example, Comparative Example 4), and when the sodium content is too high (for example, Comparative Example 5), it was found that I(400) / I(111) and I(440) / I(400) exceeded the scope of the present invention. On the other hand, it was found that for the lithium ion battery having the content ranges of aluminum and sodium of the present invention, the cycle capacity retention rate at 25°C, the cycle capacity retention rate at 45°C, and the storage capacity retention rate were all clearly improved.

[0124] From the comparison between Examples 1 to 8 and Examples 9 to 21, when the niobium element of the present invention is further contained in the positive electrode active material layer and the content C% is within the scope of the present invention, it was found that the high temperature storage performance of the lithium ion battery is further improved.

[0125] From the comparison between Examples 9 to 21 and Examples 22 to 34, when lithium nickel cobalt manganese oxide is further contained in the positive electrode active material layer, it was found that the cycle capacity retention rate at 25°C, the cycle capacity retention rate at 45°C, and the storage capacity retention rate of the lithium ion battery are further improved.

[0126] From Examples 22 to 34, although the weight fraction of cobalt in lithium nickel cobalt manganese oxide was different and affected the cycle characteristics and high temperature storage characteristics of the lithium ion battery, it was found that as long as the content of lithium nickel cobalt manganese oxide is within the scope of the present invention, a lithium ion battery with excellent cycle characteristics and high temperature storage performance can be obtained.

[0127] From Examples 37 to 41, it was found that when lithium iron phosphate is further contained in the positive electrode active material layer, the 25°C cycle capacity retention rate, 45°C cycle capacity retention rate, and storage capacity retention rate of the lithium-ion battery are further improved.

[0128] The relationships of the contents of aluminum, sodium, and niobium, namely the A + B value, A / B value, A + C value, A + B + C value, and C / B value, also usually affect the cycle characteristics and high-temperature storage characteristics of lithium-ion batteries. However, from Examples 1 to 41, it was found that as long as the parameters of the above combinations of A, B, and C are within the scope of the present invention, a lithium-ion battery with excellent cycle characteristics and high-temperature storage characteristics can be obtained.

[0129] The particle size of modified LMO, the particle size of NCM, the particle size of LFP, the content of Co in the positive electrode active material layer, the molar ratio of Ni and Mn, the molar ratio of Co and Mn, the molar ratio of Fe and Mn, and the compression density of the positive electrode active material layer also usually affect the cycle characteristics and high-temperature storage characteristics of lithium-ion batteries. However, from Examples 1 to 41, it was found that as long as the above parameters are within the scope of the present invention, a lithium-ion battery with excellent cycle characteristics and high-temperature storage characteristics can be obtained.

[0130] FIG. 1 is an XRD diagram of the positive electrode sheet powder of Example 35 of the present invention. From FIG. 1, it was found that for the positive electrode active material of the present invention, a first diffraction peak corresponding to the (111) crystal plane appears at 18° to 20°, a second diffraction peak corresponding to the (400) crystal plane appears at 43° to 45°, and a third diffraction peak corresponding to the (440) crystal plane appears at 63° to 65°, and it satisfies 0.25 < I(400) / I(111) < 0.5 and 0.35 < I(440) / I(400) < 0.55.

[0131] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Modifications, equivalent substitutions, improvements, etc. made within the scope of the gist and principles of the present invention are included in the protection scope of the present invention.

Claims

1. An electrochemical device, comprising a positive electrode, a negative electrode, a separator and an electrolytic solution, wherein the positive electrode includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector, the positive electrode active material layer contains lithium manganese oxide, and the lithium manganese oxide contains aluminum and sodium, when the content of aluminum is A% and the content of sodium is B% with respect to the weight of the positive electrode active material, A and B satisfy 0.01 ≦ A ≦ 2 and 0.001 ≦ B ≦ 1, the lithium manganese oxide further contains niobium, and when the content of niobium is C% with respect to the weight of the positive electrode active material, C satisfies 0 < C ≦ 0.9, and A and C satisfy 0.07 ≦ A + C ≦ 2.1, an electrochemical device.

2. The electrochemical device satisfies at least one of the following: (a) A and B satisfy 0.011 ≦ A + B ≦ 2.5; (b) A and B satisfy 0.1 ≦ A / B ≦ 125, which is the electrochemical device according to Claim 1.

3. A and B satisfy 0.03 ≦ A + B < 2 and 2 < A / B ≦ 125, which is the electrochemical device according to Claim 1.

4. The electrochemical device satisfies at least one of the following: (d) A, B and C satisfy 0.011 ≦ A + B + C ≦ 3.3; (e) B and C satisfy 0 < C / B ≦ 40, which is the electrochemical device according to Claim 1.

5. As measured by XRD, the lithium manganese oxide satisfies at least one of the following: (f) the lithium manganese oxide shows a first diffraction peak corresponding to the (111) crystal plane at 18° to 20°, and the peak intensity of the first diffraction peak is I(111); (g) the lithium manganese oxide shows a second diffraction peak corresponding to the (400) crystal plane at 43° to 45°, and the peak intensity of the second diffraction peak is I(400); (h) the lithium manganese oxide shows a third diffraction peak corresponding to the (440) crystal plane at 63° to 65°, and the peak intensity of the third diffraction peak is I(440), which is the electrochemical device according to Claim 1.

6. The electrochemical device satisfies the following: (i) I(400) and I(111) satisfy 0.25 < I(400) / I(111) < 0.55, (j) I(440) and I(400) satisfy 0.35 < I(440) / I(400) < 0.55, and the electrochemical device according to claim 5, which satisfies at least one of them.

7. The positive electrode active material layer further contains lithium nickel cobalt manganese oxide, and the weight fraction of cobalt is less than 15% or 15% with respect to the weight of the positive electrode active material. The electrochemical device according to claim 1.

8. The molar ratio of nickel to manganese in the positive electrode active material layer is 0.02:1 to 0.7:1, and the molar ratio of cobalt to manganese is less than 0.3:1 or 0.3:

1. The electrochemical device according to claim 7.

9. The positive electrode active material layer further contains lithium iron phosphate, and the average particle diameter of the lithium iron phosphate is smaller than the average particle diameter of the lithium manganese oxide. The electrochemical device according to any one of claims 1 to 8.

10. The molar ratio of iron to manganese in the positive electrode active material layer is 0.02:1 to 0.25:

1. The electrochemical device according to claim 9.

11. Based on the weight of the positive electrode active material layer, the weight fraction of lithium iron phosphate is ≦ 30%. The electrochemical device according to claim 9.

12. The compression density P of the positive electrode active material layer is 2.7 g / cm ３ ≤ P ≤ 4.0 g / cm ３ The electrochemical device according to claim 1, which satisfies the above conditions.

13. An electronic device including the electrochemical device according to any one of claims 1 to 12.

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